ASoC: Return -1 instead of -EINVAL to ensure consistency

The code can't really cope with I/O errors, so it would be better
to be consistent throughout all cache functions and return -1 instead
of -EINVAL.

The return value of snd_soc_read(...) is mostly checked in the probe
function and nowhere else.
Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/soc-cache.c

@@ -228,7 +228,7 @@ static unsigned int snd_soc_8_16_read(struct snd_soc_codec *codec,
 	if (reg >= codec->driver->reg_cache_size ||
 	    snd_soc_codec_volatile_register(codec, reg)) {
 		if (codec->cache_only)
-			return -EINVAL;
+			return -1;
 
 		return codec->hw_read(codec, reg);
 	} else {
@@ -455,7 +455,7 @@ static unsigned int snd_soc_16_16_read(struct snd_soc_codec *codec,
 	if (reg >= codec->driver->reg_cache_size ||
 	    snd_soc_codec_volatile_register(codec, reg)) {
 		if (codec->cache_only)
-			return -EINVAL;
+			return -1;
 
 		return codec->hw_read(codec, reg);
 	}